1. Field of the Invention
This invention relates generally to an electronic blackboard in which an electrostatic latent image is formed on a blackboard display member by an electrostatic recording head and, more particularly, to a system in which the latent image is electrostatically recorded and converted into a visible image by means of toner.
2. Description of the Background
There was previously proposed in U.S. Patent Application Ser. No. 07/201,167, filed June 2, 1988, now U.S. Pat. No. 4,908,711 issued Mar. 13, 1990, an electronic blackboard having a copy function to create a hard copy of characters that are handwritten onto a blackboard sheet and having a display function to read copy information and to display it on the blackboard sheet.
In such electronic blackboards having the display function, as shown in FIG. 1, an electronic recording medium 1 in the form of an endless sheet is arranged to be transported by a feed motor 2 and a drive roller 3.
As shown in FIG. 2, the electronic recording medium 1 includes a substrate 1a composed of a sheet of polyethylene terephthalate having a thickness of 100 microns. An electrically conductive layer 1c having a thickness of about 50 microns is composed of a polymer such as polyurethane, and adheres to the substrate 1a by means of an adhesive layer 1b having a thickness of about 10 microns. The polymer constituting the electrically conductive layer 1c contains titanium dioxide or indium oxide, is white in color, and may be derived from a mixture of diisocyanate and polyethylene glycol.
A dielectric layer 1e having a thickness of about 25 microns and made of transparent polyvinylidene fluoride adheres to the conductive layer 1c by means of an adhesive layer 1d having a thickness of about 10 microns. An ultraviolet light ray absorber is contained in the adhesive layer 1d. It is noted that polyvinylidene fluoride is a substance that generally cannot be adherent by means of regular adhesives, so a special pressure-sensitive adhesive is used.
Further, a hard coat layer 1f is applied to the surface of the dielectric layer 1e, and the surface of the hard coat layer 1f may be used as a write surface W for the electrostatic recording medium 1. A commercial product known as "Tough Top" marketed by the Toray Corporation and made of a resin of a polysiloxane type can be used for the hard coat 1f. Consequently, damage to the write surface W can be prevented and letters or the like written on the write surface can be easily erased.
A recording head 6 composed of a write electrode, a stylus electrode portion 4, and a control electrode portion 5, an AC charge remover 7, a cleaning blade 8, a charge coupled device (CCD) line sensor 10, a lens system 9, and a mirror 11 are all arranged in opposing relation to the endless electrostatic recording medium 1. A developer roller 12 is further provided for supplying toner.
The electronic blackboard assembly is encased by a cover (not shown) having a window or aperture in a front portion thereof, with the electrostatic recording medium 1 being exposed through the window. Provided in a lower portion of the front portion of the cover is an original document insertion slot 14a, a copy ejection slot 14b, and an outlet slot 15 for printed paper. Although not shown, the cover is supported on rollers so that the electronic blackboard is easily transportable.
In normal use of this electronic blackboard, information may be written on the write surface W of the electrostatic recording medium 1 with, for example, a felt pen or the like. When it is desired to copy the written information, the exposed portion of the electrostatic recording medium I is driven to a rear portion of the blackboard so that information written thereon can be read by the CCD line sensor 10 through the mirror 11 and the lens system 9. The visual information is converted into electrical signals by the CCD line sensor 10 and copied onto recording paper by, for example, xerography or a similar process, and the printed copy is discharged from the printed paper outlet slot 15. When it is desired to electrostatically display the image of an existing document on the electronic blackboard, the document is inserted through the document insertion slot 14a, and an electrostatic latent image is formed on the write surface W of the electrostatic recording medium 1 by the recording head 6. The latent image is developed by the toner supplied from the developer roller 12, and adheres to the electrostatic latent image on the write surface W as it passes the developer roller 12, resulting in a visible image (toner image). As the recording medium 1 travels past the rear portion of the blackboard, toner and ink marks written on the recording medium 1 with the felt pen are scraped away by the cleaning or doctor blade 8, and any charges or electrification on the write surface W of the recording medium 1 are removed by the AC charge remover 7.
While providing an operable system, such a conventional device as mentioned above, nevertheless, has various defects such as the following. (1) Since the toner merely electrostatically adheres onto the electrostatic recording medium 1, toner drop may occur, causing clothing and the surrounding area to be contaminated therewith. (2) Toner particles may be scattered by cooling fans, air conditioning, and breezes, thereby further contaminating the environment. (3) With a standard printer associated therewith, the size of the copy paper may be limited, so that the size of the hard copy image may have to be reduced.